This is a gaming term for a cleric of nature. Druids tend to not be affiliated with any church, but protects an area of land seeking to keep it from being 'harmed' by those of civilized disposition. Druids are represented in different ways in different games.
Historic information: A Druid is specifically a member of the religion of the ancient Celts. Historic tales present Druids as being able to accomplish some rather fantastic feats. Seeking to claim such power for themselves, by reputation if not fact, modern groups will claim a Druid connection.